Digital servo track format with leading and trailing identifiers

ABSTRACT

A digital servo track pattern for a magnetic medium which can be recorded and reproduced by a recording and reproducing system. The servo track pattern has a plurality of digital mark patterns recorded thereon, each of said digital mark patterns having a leading identifier field of digital bits, a trailing identifier field of digital bits and a field of digital synchronizing data located between said leading and trailing identifier fields. The leading identifier field of digital bits is electrically equivalent during reproducing while the medium is moving in a first direction to the trailing identifier field of digital bits while the medium is moving in a direction opposite to said first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 07/843,511 filed on Feb.28, 1992 now issued as U.S. Pat. No. 5,408,368.

Data Recording System having Demarking Capability and Method, by LionelShih, filed Feb. 28, 1992, Ser. No. 07/843,522, now U.S. Pat. No.5,319,504.

Data Recording System having Logical Overrecording Capability, by LionelShih, filed Feb. 28, 1992, Ser. No. 07/843,454, now allowed.

Data Recording System having Unique End-of-Recording andStart-of-Recording Format Indicators, by Tracy Wood and Lionel Shih,filed Feb. 28, 1992, Ser. No. 07/843,585, now U.S. Pat. No. 5,384,668.

Data Recording System having Recording Partition Groups, by Lionel Shih,filed February 28, 1992, Serial No. 07/843,448 now abandoned.

Data Tape Recording System having Longitudinal Address and Servo Tracks,by Lionel Shih and Tracy Wood, filed Feb. 28, 1992, Ser. No. 07/843,995now abandoned.

Data Recording System having Improved Bookkeeping Capability, by LionelShih and John Haglund, filed Feb. 28, 1992, Ser. No. 07/843,461 nowallowed.

Data Recording System having Improved Automatic Rewrite Capability andMethod of Rewriting, by Lionel Shih, filed Feb. 28, 1992, Ser. No.07/843,449 now U.S. Pat. No. 5,341,378.

Data Recording System having Improved Longitudinal and Helical SearchCapability, by Lionel Shih and Jerry Holter, filed Feb. 28, 1992, Ser.No. 07/843,740 now allowed.

Volume Format Table for Data Recording System, by Lionel Shih, filedFeb. 28, 1992, Ser. No. 07/843,532.

Digital Servo Track Format, by Kurt Hallamasek, filed Feb. 28, 1992,Ser. No. 07/843,511 now U.S. Pat. No. 5,408,368.

Longitudinal Track Format for Data Recording System, by Jeffrey Fincher,Kurt Hallamasek and Keith Kambies, filed Feb. 28, 1992, Ser. No.07/843,723 now U.S. Pat. No. 5,341,251.

Data Recording System having unique Nonrecording Detection, by LionelShih and Tracy Wood, filed Feb. 28, 1992, Ser. No. 07/843,517 now U.S.Pat. No. 5,335,119.

Triple orthogonally Interleaved Error Correction System, by KirkHandley, Donald S. Rhines and William McCoy, filed Jan. 13, 1992, Ser.No. 07/820,737 now U.S. Pat. No. 5,335,119.

FIELD OF THE INVENTION

The present invention relates to mass storage devices, and moreparticularly, to recording and reproducing apparatus and methods forachieving very high density recording of digital information at veryhigh transfer rates.

BACKGROUND OF THE INVENTION

The market for mass storage devices is growing at what seems to be anever increasing rate with the sales of high-performance computerspenetrating numerous industries ranging from financial institutions tooil exploration companies. The processing power of thesehigh-performance systems, and the data they generate, are increasingfaster than the ability of storage devices to keep pace. The problem ofdata storage and rapid retrieval is particularly pronounced incomputational-intensive applications which create huge amounts of datathat need to be accessed in seconds rather than minutes, hours or evendays.

Magnetic disks remain the preferred media for direct access tofrequently used files because of their fast access times. However,because of their high cost per-unit of storage (such as a megabyte) andtheir limited capacity, magnetic disk recorders are prohibitivelyexpensive and therefore impractical for large-scale data storage. Withthe advances in magnetic tape technology, tape based systems remain thepreferred choice for mass data storage. In addition to cost, magnetictape exceeds the storage density of any other medium, at least from avolumetric standpoint, because tape is a much thinner medium than, forexample, magnetic disks, and tape can be tightly packed. A generaldiscussion of such technology may be found in Mass Storage Technologies,by S. Ranada, published in 1991 by Meckler Publishing.

The tape format basically defines the recording path used to recordsignals on the tape. There are many different recording formatsdeveloped for data recording and reproducing. A commonly used format forhigh capacity systems is IBM's 3480 multi-track tape cartridge format inwhich the tape transport employs a stationary head and records dataalong longitudinal tracks. Since the late 1970's rotary head helicalscan recorders, a technology developed originally for video recorders,have been used for recording data. In helical scan recorders, the tapeis transported past a rapidly rotating head along a helical path wherebydata is recorded diagonally across the tape. Compared to longitudinalrecorders, helical scan recorders generate high recording densities andlower tape speeds for a given data transfer rate.

SUMMARY OF THE INVENTION

The present invention is directed to a magnetic recording andreproducing system that is particularly suited for helical recorders ofthe type which utilize cassettes of tape having two hubs and an outershell, but is not limited to helical recorders or to the use of suchcassettes.

However, because of the unique recording format used by the system, thecassettes can be conveniently loaded on and unloaded from the system atany of many positions along the length of tape in the cassette withoutjeopardizing the integrity of the data recorded on the tape. Because ofthis functionality, the system can conveniently use cassettes ofdifferent sizes and different lengths of tape, and the necessity ofrewinding the tape to the beginning of the tape prior to unloading andloading is obviated.

While the system disclosed herein is particularly suited for providingarchival recordings of data and may be a backup to a network computerapplication having a large file server, the system disclosed herein isalso suited for use as a near-line library when used in combination witha large computer disc drive with the disc drive interacting with thesystem to perform frequent and multiple transfers of data between thesystem and the disc drive. The present system is also particularlysuited for a library functionality which may be a repository formultiple disc drives and may use robotics for loading and unloadinghundreds if not thousands of cassettes during use. It is particularlyadvantageous that the system utilizes cassettes having extremely highcapacity which may be on the order of 165×109 bytes for large cassetteshaving maximum tape lengths. The system also exhibits extremely highdata transfer rates, i.e., on the order of 15 megabytes per second.

While the system disclosed herein is advantageously suited for use withcassettes of tape, it should be fully understood that the system doesnot require such cassettes and can be used with reels of tape, albeitnot with all of the attendant advantages and desirable features. Theformat and functionality that is disclosed has applicability to a widerange of recorders and is also not limited to a magnetic recordingmedium. Many of the desirable attributes of the system are applicable totypes of recording other than helical type recording, such aslongitudinal recording systems, and many aspects of the present systemare definitely not limited to helical type recording and reproducingapparatus and systems.

Also, while the system is described herein as a recording andreproducing system, it should also be understood a machine could be madewhich could have only the functionality of a recorder or of a playbackor reproducing machine. Such limited function machines would severelylimit the advantages of a system having both recording and reproducingcapabilities, and any cost savings of such limited function machines isnot contemplated to be justified in light of the limitations that wouldresult.

More particularly, the present invention is directed to a magneticrecording and reproducing system that has a recording format thatrecords blocks of data of predetermined size as specified by a host oruser system and the present system reformats the user data blocks intophysical blocks that are recorded on tape, with the physical blocksbeing recorded in what are referred to herein as double frames. Eachdouble frame is recorded on a set of successive helical tracks,preferably 32 tracks. Each double frame has system format datainterleaved with the user data block data which system format dataidentifies the double frame as being of a particular type.

The present invention is directed to a digital servo track pattern for amagnetic medium which can be recorded and reproduced by a recording andreproducing system. The servo track pattern has a plurality of digitalmark patterns recorded thereon, with each of the digital mark patternshaving a leading identifier field of digital bits, a trailing identifierfield of digital bits and a field of digital synchronizing data locatedbetween said leading and trailing identifier fields. The leadingidentifier field of digital bits is electrically equivalent duringreproducing while the medium is moving in a first direction to thetrailing identifier field of digital bits while the medium is moving inthe opposite direction. The symmetry of the mark patterns enable thesystem to recover the mark pattern with the same recovery timeregardless of whether the tape is being moved in the forward or reversedirection.

A mark pattern is written along the servo track for each pair of helicaltracks, and a first predetermined-one of the mark patterns defines thefirst track pair of the double frame, a second one of the mark patternsdefines the middle track pair of the double frame, a third one of themark patterns alternates with the first one and defines every otherdouble frame. The fourth predetermined mark pattern is used for allother track pairs.

OBJECTS OF THE INVENTION

It is a general object of the present invention to provide an improvedsystem having the desirable aspects of helical recording on magnetictape contained in cassettes which is uniquely configured to recorddigital data utilizing a format that contributes to extremely highcapacity recording, reliable recording and reproducing, and reliablesearching and access to data that is recorded on the tape.

It is an object of the present invention to provide an improved servotrack pattern for use in a recording and reproducing system which hasmany advantages.

Another object of the present invention is to provide an improved servotrack pattern that comprises a digital signal that not only providesreliable servo marks but which contains other relevant information.

Still another object of the present invention is to provide such animproved digital servo track pattern that is uniquely defined to havethe same recovery time during reproducing regardless of the direction oftape movement.

Yet another object of the present invention is to provide such animproved servo track pattern, which because of its unique design,enables a single electrical circuit to obtain the same signal regardlessof the direction of tape movement.

Other objects and advantages will become apparent upon reading thefollowing detailed description, while referring to the attacheddrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the present system shown togetherwith a host system and an intelligent peripheral interface that islocated between the host system and the present system;

FIG. 2 is a broad functional block diagram of the system disclosedherein;

FIG. 3 is a schematic diagram illustrating the manner in which user datais organized and the manner in which the system disclosed hereinorganizes and formats the user data for recording and reproducing by thesystem;

FIG. 4 is a more detailed functional block diagram of the systemdisclosed herein;

FIG. 5 schematically illustrates a magnetic tape and formatcharacteristics that are used by an embodiment of the system arranged torecord and reproduce information data on magnetic tape;

FIG. 6 is a front elevation of the manual operator control panel of thesystem disclosed herein;

FIG. 7 is a schematic illustration of a segment of magnetic tape andillustrating the format of various recording areas and tracks which areutilized by an embodiment of the system arranged to record and reproducedata in a rotary head helical scan magnetic tape recorder;

FIG. 8 is a schematic illustration of a segment of tape, similar to thatshown in FIG. 7, but particularly illustrating the format of recordedsegments in the various recording areas and tracks of the tape;

FIG. 9 is a schematic illustration of sets of recorded double framesthat are recorded during various recording operations that can beperformed by the system;

FIG. 10 is a schematic illustration of a tape, with portions removed,and illustrating the location of partitions formatted on the tape;

FIG. 11 is an illustration of the organization of data that is recordedin the helical recording area of a tape;

FIG. 12 is a chart illustrating the organization of the subarea sectionused to record system format data shown in FIG. 11;

FIG. 13 is a schematic illustration of the organization of data that isrecorded in each segment of the logical address track (LAT) and physicaladdress track (PAT) shown in FIGS. 7 and 8;

FIG. 14 is a chart showing the type of segment information that isrecorded in various logical address track segments and in the variousphysical address track segments, and illustrating the relationship ofthe segment information to the type of information that is recorded onthe helical recording area;

FIG. 15 illustrates a chart of the information that is recorded in thevarious types of logical address track segments and physical addresstrack segments;

FIG. 16 is a diagram illustrating the front padding portion of theillustration shown in FIG. 13;

FIG. 17 is a diagram illustrating the rear padding portion of theillustration shown in FIG. 13;

FIGS. 18(a), 18(b), 18(c) and 18(d) illustrate the waveform of varioussynchronization digital information that is recorded on the servo track;

FIG. 19 is a chart illustrating the type of digital information that isrecorded at various locations within each servo track segment;

FIG. 20 is a chart illustrating the information that is recorded in thehelical track type field (HTTY) at the byte 29 location of the physicalblock information in FIG. 21;

FIG. 21 is a chart illustrating the physical block information that isrecorded in subblocks 0, 2 and 4 of the subarea as shown in FIGS. 11 and12;

FIG. 22 is a chart illustrating the volume format information that isrecorded in subblock 1 of the subarea as shown in FIGS. 11 and 12;

FIG. 23 is a chart illustrating the information that is recorded in theformat identifier field (FID) at the byte 0 location of the physicalblock information in FIG. 21;

FIG. 24 is a chart illustrating the information that is recorded in avolume format table (VFT) located in the VFI zones shown in FIG. 10;

FIG. 25 is a chart illustrating the information that is recorded in atable entry in the volume format table (VFT) shown in FIG. 24;

FIG. 26 is a chart illustrating the information that is recorded in anend of volume (EOV) entry in the volume format table (VFT) shown in FIG.24;

FIGS. 27(a) and 27(b) comprises a glossary of terms and acronyms,together with a brief description of them, used herein to describe themethods and apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Broad Overview of the System

While the present invention will be specifically described in connectionwith a rotary head helical scan tape recording apparatus, it is equallyapplicable to other types of recording apparatus, such as a diskrecorder or a longitudinal or quadruples-type tape recorder.Additionally, while the present invention will be described inconjunction with the recording and reproducing of information onmagnetic tape with the use of electromagnetic transducing heads, thepresent invention is also applicable to optical recorders or the likeusing appropriate transducers and recording mediums.

It should also be understood that the present invention is applicable toarrangements where the rotating record and/or reproduce head can move ineither rotational direction, where the tape can be introduced to thehelical path either above or below the exit point from the path andwhere the tape can be transported about the helical path in eitherdirection.

The system or apparatus disclosed herein can also be referred to as adata storage peripheral that is a high speed, high density helical scantape recording and reproducing device that is designed to be operated ina master/slave environment as defined by the Intelligent PeripheralInterface (IPI) standards, such as ANSI X3.147-1988 (ANSI is theAmerican National Standard Institute) and ANSI X3T9/88-82, Revision 2.1,Jan. 3, 1989. The system provides the functionality of an IPI-3 slave,as illustrated in FIG. 1.

The system, indicated generally at 20, is an addressable entity undercontrol of and is connected to an IPI master 22 that is resident in ahost system 24. The host system IPI master 22, which is not describedherein, is responsible for managing the system 20 as well as other IPIslaves in accordance with the capabilities thereof and is responsiblefor controlling the IPI interface.

Referring to the broad functional block diagram of FIG. 2, the system 20has the capability to accept commands and data from and transferresponses and data to the host system 24 (FIG. 1) connected to acomputer interface port 26 and the system 20 has a cassette interface 28through which tape cassettes 30 having tape loaded thereon can beaccepted and ejected. When a cassette is inserted into the cassetteinterface 28, the system automatically loads the cassettes bypositioning the cassette over the capstan hubs, thereafter extractingtape from the cassette and threading it over the longitudinal read/writeheads (not shown). When necessary, the tape is also threaded over therotatable read and write heads that record data on and reproduce datafrom tracks that extend diagonally across the tape as it is transportedabout a cylindrical guide drum. The rotatable heads and tape guide arecommonly in an assembly referred to as a scanner, which is functionallyillustrated at 32.

The structure of the scanner 32 shown functionally as well as thecassette interface 28, which are functionally illustrated in FIG. 2, arenot in and of themselves part of the present invention, but are known inthe art. The scanner includes a pair of axially displaced drum sections,one of which is stationary and the other rotatable. The rotatable drumsection has four orthogonally located read heads positioned on its outerperiphery, with four write heads located immediately adjacent thereto.The read heads are mounted on electromechanical bender elements so thatthey can be laterally positioned relative to a track to more accuratelyfollow the track during reproducing and to locate the heads on a trackadjacent a track that would be recorded by the write head duringrecording so as to obtain the data immediately after it has been writtenfor the purpose of verifying that the data has been accurately recorded.Details of the scanner are described in Ampex D2 VTR manual, which isspecifically incorporated by reference herein.

When commanded to eject a cassette, the system unthreads the tape fromthe helical scanner if it had been threaded over the same, and alsounthreads the tape from the longitudinal heads and retracks the tapeback into the cassette which is then ejected from the cassette interface28.

The system includes a manual interface 34 that contains switches andindicators necessary for an operator to power on and configure thesystem and also contains controls and indicators that are necessary foran operator to manually initiate loading and ejecting a cassette. Thecassette interface 28 allows tape cassettes to be inserted in andremoved from the system 20. The cassette interface is located in thefront of the system. The cassette interface 28 provides the capabilityto accept small, medium and large D-type tape cassette sizes asspecified in the Society of Motion Picture and Television Engineers(SMPTE) 226 M standard.

A control function block 36 controls the operation of the system and itis shown to have lines 38 for connecting to an auxiliary interface thatis primarily used to execute diagnostic test sequences and predefinedself-tests. The control function 36 is connected to a format functionblock 42 that formats the data received from the computer interface portand is directed to an encoding function block 44 for encoding andsubsequent recording on the tape. Also, data recovered duringreproducing is applied to a decode function block 46 that decodes thedata, applies it to the format function block 42 for transfer to thehost system 24 via the computer interface port 26. Commands received bythe system 20 from the host system 24 are input through the computerinterface port 26 and are routed to the control function 36 forprocessing and subsequent execution.

In accordance with an important aspect of the system, it accepts userdata from the host system 24 in an organizational data structure definedby the host system, and the system disclosed herein formats the userdata in a manner that enables the data to be recorded on and reproducedfrom tape using a format that enables effective fast access to data andwhich facilitates very high data transfer rates as well as very highdata capacities. The manner in which the system interacts with a hostsystem supplying user data can be more easily understood by referring toFIG. 3 which shows the user view constructs to the left of a referenceline 50 with the recording media view constructs being shown to theright of the line 50. Referring initially to the user view of the data,the user or host system generally has data contained in file sets whichmay include one or more files 52, with each of the files having one ormore file sections 54. Each of the file sections 54 may have a largenumber of data blocks 56 in them with the data blocks having a size thatis determined by the user or host system and which may comprise aconvenient amount of data which is formatted by the system 20 forrecording.

The present system 20 will support data blocks 56 having as few as 808-bit bytes, up to approximately 1 million bytes. The system 20 receivesthe data blocks 56 and organizes them into physical blocks 58 of dataand the physical blocks are recorded in one or more partitions 60located on the tape with the partitions being located in a volume 62that may be part of a volume set. However, each volume 62 represents asingle cassette of tape.

During the recording of user data, user data blocks are formatted intophysical blocks by the system 20. Depending upon the size of the datablocks, which may not exceed the amount of data that is contained in aphysical block, i.e., only complete data blocks can be contained inphysical blocks and a data block cannot extend Pver more than onephysical block, there may be a number of data blocks contained in aphysical block. The system supports up to 1,199,840 bytes of user datablock data in a physical block.

In accordance with another aspect of the present system, the units orphysical blocks 58 that are recorded by the system 20 are defined by thesystem to be of a predetermined size and that size is recorded andreproduced by the system in units that are defined as double frames.While there are various types of double frames, as will be described,the size of all of the types of double frames are the same and arerecorded on a helical recording area by the scanner 32 during recording.Each double frame consists of a set of consecutive helical tracks, withthe set preferably comprising 32 helical tracks. Given the fact thatwhole user data blocks 56 must be formatted into physical blocks, andthe size of the user data blocks are user defined and can be different,it should be evident that the amount of data in integer numbers of wholedata blocks that can be grouped into a physical block may not completethe entire 1,199,840 bytes of the physical block. In such event, thesystem 20 pads out the physical block with bytes of filler data in orderto reach the total capacity of the physical block.

With the above format discussion in mind, a physical block is fullydefined by seven recorded parameters which are used to identify the userdata that is recorded and reproduced by the system 20 in its format.These parameters include a file section number (FSN), a first data blocknumber (FDBN), the cumulative data block number (CDBN), a datablock/byte identification (DB/B), a data block check sum enabledindication (DCSE), a data block size (DBS) and a total byte count (TBC).

With respect to the above, the file section number will identify thefile section of data which is located in the physical block and eachfile section may span many physical blocks. The first data block number(FDBN) number identifies the ordinal number of the first data blocknumber of a physical block in a file section which is being recorded.The cumulative data block number represents the ordinal number of thefirst data block or first user data byte of a physical block countingfrom the first data block of a partition. The data block/byte indicationmerely refers to whether the data is organized into files or not. Sincethe system 20 is also useful as an instrumentation recorder which mayhave a continuing stream of data that is to be recorded with no logicalboundaries in the data, the use of a predetermined number of bytes isalso supported by the system. The data block size is defined by the hostor user system 24 and as previously mentioned, can be a size that is upto thee total capacity of the physical block which is 1,199,840 bytes.In the present system, physical blocks are of one size and are recordedby the system on 32 successive helical tracks, with the physical blockdata being recorded as double frames of data.

In accordance with another important aspect of the format that is used.by the system 20, there are several different types of double frames,with the type of double frame being recorded with the user data. It isalso an important attribute of the system that the system record theuser data with the tape moving during the recording process. The systemdoes not stop the tape to re-record a physical block that may havefailed the read-while-write verification criteria of the system. Rather,if during the recording process, a recorded track is reproduced andfound unacceptable when subjected to an error analysis, the systemrecords that same physical block downstream on the tape, and dependingupon how early the verification failure was determined, will invalidateany inaccurate physical block and possibly the following physical block,and will rewrite, i.e., rerecord the invalidated physical block andpossibly the following one. The subsequent physical block can berecorded only if the preceding physical block is successfully recorded.

More particularly, the format of the types and use of double frames bythe system include seven types, each of which have format dataassociated with the double frame that uniquely identifies it as a doubleframe of that type. The seven types include: (1) a BOM double framewhich is used in the beginning of a partition on tape; (2) a physicalblock double frame (PB DF) which is used to record user data in thephysical block form, and system format information; (3) an end ofrecording/temporary double frame (EOR/T) which is used to identify atemporary and successful end of recording; (4) an end of recording/error(EOR/E) which is used to identify a failed write, i.e., a previouslyrecorded physical block was checked for errors and did not satisfy theverification criteria; (5) an end of recording double frame (EOR) whichis used as a logical file mark which indicates the end of a successfulrecording of file marks; (6) a demark double frame (DMDF) which is usedto indicate that the preceding physical block double frame has failedverification criteria; and, (7) an amble double frame (AMDF) which isused to begin a recording, particularly one in which a gap is desiredbetween old and new recording to prevent damage to existing data. Theuse of the various types of double frames greatly contribute to thepowerful functionality of the system as will be described.

Detailed Functional Block Diagram of the System

While the system has been broadly described with respect to the broadfunctional block diagram of FIG. 2, the system will now be described inmore detail in connection with the detailed functional block diagramshown in FIG. 4. The system 20 provides the capability of recording orwriting data on a tape at a specified address that can be selected bythe host system 24. The system 20 accepts data blocks from the hostsystem 24 across one of the computer interface ports, such as the port26 shown in FIG. 2, and the interface ports are connected to aninterface selector function block 70. While a second computer interfacecan be optionally provided, the selector interface function block isprovided to route data across one of multiple computer interface portsto a data formatting function block 72. The data is then applied to anencode/decode function block 74 where the data is preferably encodedwith a C1, C2 and C3 error correction code so that errors can bedetected and corrected during a subsequent reproducing operation. TheC1, C2 and C3 error correction code is not described herein, but isfully described in the above cross-referenced related application ofKirk Handley, Donald S. Rhines and William McCoy, entitled TripleOrthogonally Interleaved Error Correction System, Serial No. (3661),filed Jan. 13, 1992, which is specifically incorporated by referenceherein.

The data format function block 72 also includes a data buffer for thephysical block data and it has the capability of buffering a minimum of48 formatted physical blocks. The data format function block 72 managesthe buffer in a way which anticipates that there will be bufferunderruns and buffer overruns. The data format function block 72 acceptsone or more data blocks depending upon the size of the data blocks whichis specified by the host system and which can range from 80 bytes to1,199,840 bytes. obviously, the larger the data blocks, the fewer can befit into a physical block. The data formatting function 72 formats thedata blocks into fixed size physical blocks and only an integer numberof data blocks are contained in a physical block, since a data blockcannot span a physical block boundary. If necessary, the data formattingfunction block 72 inserts fill data into the physical block to completethe required physical block format size. During a recording or writeoperation, the data formatting function 72 transfers formatted physicalblocks to the encode/decode function block 74 but retains a givenphysical block in the buffer until such time as the encode/decodefunction 74 indicates that the physical block was correctly written ontape.

During a read or reproducing operation, the data format function block72 accepts physical blocks from the encode/decode function block 74 anddiscards any fill data that was inserted into the physical block duringa recording operation. The data format function block 72 reconstructsthe original data blocks from the formatted physical blocks. The dataformatting function 72 uses the physical block buffer to perform exactlogical positioning to a specified data block number address. The dataformatting function 72 then transfers the data blocks to the interfaceselector function block 70.

During recording the encoded data is then transferred from theencode/decode function block 74 to a read-while-write function block 76which enables the system to support a rewrite or re-recording capabilityin the event that an unacceptable number of errors are detected. Thereadwhile-write function block 76 necessarily decodes the data that isreproduced to determine if the data written on the tape passesverification criteria. If an unacceptable error level is detected, theread-while-write function block 76 causes the original the double frameto be rewritten on the tape. The system has read channels fortransferring the data recovered during reproducing and write channelsfor transferring the data for recording on tape.

The read-while-write function block 76 analyzes the data read from thehelical tracks to determine if a physical block needs to be rewritten.During a write operation, the read-while-write function block 76 acceptsencoded data from the encode/decode function 74 on the write channelswhile simultaneously accepting encoded data from the channel formattingfunction block 78 on the read channels and buffered by theread-while-write function block 76. The block 76 retains a physicalblock until such time that the data has been written on tape, thereafterread from tape and analyzed to determine if it passes the verificationcriteria. The read-while-write function block 76 then initiates arewrite operation by interrupting the logical sequence of writing, butnot tape motion, and rewriting the entire physical block using theoriginal buffered data.

If the rewritten physical block does not pass the criteria, it will berewritten again until it is successfully written, but only attempts amaximum of 20 rewrites, with the number being adjustable by the hostsystem between zero and 20. If the read-while-write function block 76exhausts the rewrite attempt threshold, the write operation is thenterminated and a permanent write error is declared. During a read orreproducing operation, the read-while-write function block 76 isdisabled in that the encoded data received from the channel formattingfunction block 78 on the read channel is transferred directly to theencode/decode function block 74 on the read channel. Theread-while-write function block accepts control information from andtransfers status information to a process control function block 84.

The data from the read-while-write function block 76 is then applied toa channel format function block 78 which reformats the encoded data andadds synchronizing data. The data from the channel format function block78 is then applied to a data I/O function block 80 writes the serialdata on tape. The data I/O function block 80 also simultaneously readsthe serial data from the tape in order to support a rewrite capability,and it does so by reformatting the serial data into the encoded serialchannel data and sends it to the read-while-write function block 76. Theread-while-write function block decodes the recovered data to determineif the data written on the tape is acceptable.

During a write operation, the data I/O function block 80 accepts anencoded serial data stream from the channel formatting function block 78on the write channels, while simultaneously accepting data from thehelical scanner and transferring the data to the channel formattingfunction 78 on the read channels. The data I/O function provides lineequalization and it also provides the helical scanner subsystem,including the record amplifiers, play preamplifiers, and channelequalizers that are necessary to transfer data signals to the writeheads and accept data signals from the read heads. Activation anddeactivation of the write and read heads is also controlled by the dataI/O function block 80. It provides the capability to activate the readheads during a write operation, to support the read-while-write and therewrite capability. During a read and write operation, the data I/Ofunction 80 accepts data from the helical scanner read heads an-.dtransfers the data to the channel formatting function 78 on the readchannels. The rotation of the rotatable heads and transport of tape arecontrolled such that the scanner rotation opposes the direction of tapetransport during normal write and read operations and it accepts controlinformation and transfers status information to the transport controlfunction 90.

The channel format function block 78 accepts encoded parallel dataduring a write operation from the read-while-write function block 76 onthe write channels while simultaneously accepting encoded serial datafrom the data I/0 function 80 on the read channels. The channelformatting function block 78 inserts synchronization sequences and othersequences. The channel format function block 78 converts the paralleldata into a serial data stream, and preferably encodes the serial datastream in accordance with the MillerSquared encoding rules to favorablyshape the record data spectrum. The Miller-Squared encoding rules arewell known in the art and are also disclosed in U.S. Patent Re. 31,311,assigned to the same assignee as the present invention.

The channel formatting function block 78 then transfers the encodedserial data stream to the data I/O function block 80 on the writechannels. During a read and write operation, the channel formattingfunction accepts encoded serial data stream from the data I/O function80 on the read channels. It then provides line equalization for theserial data stream and any necessary control signals. The channelformatting function then decodes the Miller-Squared channel code to NRZdata and detects the synchronization sequences. It then converts theserial data stream into the original parallel data format. It uses thedetected synchronization sequences to identify the components of thetape format and removes the synchronization sequences and othersequences from the parallel data. The channel formatting function blockthen transfers the encoded parallel data to the read-while-writefunction block 76 on the read channels. It accepts control informationand transfers status information to the process control function 84.

A reference generator block 82 provides the timing control referencesignals to support the control of the data flow together with servocontrolled subsystems of the system. A process control function block 84provides overall control of the encode/decode function block 74, theread-while-write function block 76 and the channel formatting functionblock 78 as well as the reference generator function block 82. Theprocess control function block 84 transfers control information to andaccepts status information from the encode/decode function block 74, theread-while-write function block 76, the channel formatting functionblock 78, the reference generator function block 82 and a transportcontrol function block 90. It also accepts commands from and transfersresponses to the control function block 36.

The system 20 provides the capability of reproducing data from the tapeat a host system specified address and does so by positioning the tapeto a specified location and begins reading the data from the tape viathe data I/O function block 80. The encoded data is then decoded by theencode/decode function block 74 and errors are corrected within thecapability of the C1, C2 and C3 error correction code. If anencode/decode function block 74 error level threshold is exceeded, thesystem 20 re-reads the data. The decoded physical block data is thenreformatted back into the original data blocks by the data formattingfunction 72 and sent to the host system 20 across the computer interfaceport 26.

The system 20 provides the capability of accepting a tape cassette wheninserted into the cassette interface 28. A cassette handler functionblock 86 puts the tape cassette into the system and physically positionsthe cassette over its capstan hubs. A tape handler function block 87extracts the tape from the cassette and threads it over longitudinalread/write heads and the rotatable read/write heads which are locatedwithin a longitudinal track function block 88 and the data I/O functionblock 80, respectively. The tape handler function block 87 includesservo controlled subsystems necessary to protect and control the tapeand the rotatable head motion. It includes a read/write head rotationservo subsystem that phase locks the motion of the head drum to areference provided by the reference generator function block 82.

The head rotation servo subsystem controls the helical scanner such thatit maintains a steady state rotation speed during normal write and readoperations. The head rotation servo subsystem provides rotationalposition information, with respect to the read and write heads, forproper commutation of the signals transferred to and from the read andwrite heads. The tape handler function block 87 includes a capstan/reelmotor servo subsystem to insure proper tension of the tape and thatsubsystem dynamically positions the tape in a linear manner based uponcontrol signals received from the reference generation function block 82and control information received from the transport control functionblock 90.

The capstan reel motor servo subsystem provides the capability todynamically position the tape at various system defined speeds,including (1) pre-striped speed, (2) shuttle speed, (3) a longitudinalsearch speed, (4) a helical search speed, (5) a write speed, and (6) aread speed. The capstan reel motor servo subsystem provides a controlmeans of transitions between different tape speeds and supportspositioning based upon tape footage, physical address and logicaladdress data. The tape handler function block 87 includes athread/unthread servo subsystem to extract tape from a cassette and italso supports the function of retracting the tape into a cassette. Thethread/unthread servo subsystem physically positions the tape in thetape guide path for tape motion preparation. It also supports twophysical tape path configurations (1) a load configuration where thetape is physically positioned over the longitudinal heads and not therotatable heads, and (2) a thread operation where the tape is physicallypositioned over the longitudinal heads and is wrapped around thecylindrical tape guide of the scanner. The tape handler function block87 performs servo control of the lateral position of the rotatable readhead relative to the diagonal tracks to compensate for track pitchvariations.

The cassette handler function block 86 comprises the electromechanicalsubsystem necessary to accept, physically position and eject the tapecassettes. It senses the presence of a tape cassette inserted into thecassette interface. The cassette handler function block 86 determinesthe tape cassette size and it also identifies the tape cassetteconfiguration based on the tape cassette holding holes. By accepting atape cassette, the cassette handler function block unlocks and opens thecassette lid and physically positions the tape cassette on thecapstan/reel motor servo subsystem. Upon ejecting a tape cassette, thecassette handler function block 86 closes and locks the cassette lid andphysically removes the tape cassette from the capstan reel motor servosubsystem. The cassette handler function block accepts controlinformation from and transfers status information to the transportcontrol function block 90.

The longitudinal track function block 88 processes the information thatis written to and read from three longitudinal tracks of the tape. Thelongitudinal track function block 88 supplies the information from thelongitudinal tracks to facilitate the dynamic positioning of the tape,including searching for various physical and logical address parameters.As will be comprehensively set forth herein, physical address parametersrelate to discrete positions on the tape whereas logical addressparameters relate to the data that is recorded on the tape. Thelongitudinal track function block 88 provides the capability toindependently activate and deactivate each of the three longitudinaltrack heads. The longitudinal track function block 88 writes thenecessary control information in accordance with the system formatcriteria in the longitudinal servo control track during a writeoperation and/or a pre-format operation. The system 20 does notoverwrite previously written control information located in thelongitudinal servo control track if the tape was preformatted orprestriped. During a position or search operation, the longitudinaltrack function block 88 provides the longitudinal servo control trackinformation to the tape handler function block 87 for position andvelocity feedback. It accepts control information from and transfersstatus information to the transport control function 90.

Tape position control information is written to and written from thelongitudinal tracks by the longitudinal track function block 88. Thetransport control function block 90 provides overall control of thecassette and the tape during all operations and the manual interface 34is used to provide operator controlled manual operation of the system2Q. The transport control function block 90 transfers controlinformation to and accepts status information from the data I/O functionblock 80, the tape handler function block 87, the cassette handlerfunction block 86 and the longitudinal track function block 88. It alsoaccepts commands from and transfers responses to the processing controlfunction 84. It also provides an interface to the manual interface 34.The transport control function block 90 does not perform any operationin response to a command received from the manual interface 34 otherthan formatting and transferring the command to the control functionblock 36 via the processing control function block 84.

A data pattern generator/verifier function brock 94 is provided togenerate and/or accept downloaded data blocks which are normally routedthrough the interface selector function block 70 to the blocks 72, 74,76, 78 and 80, in order to simulate write operations. The function block94 has the capability of accepting "loop back" data blocks that havebeen processed through the system and compare the "loop back" datablocks to the original data blocks to confirm proper operation.

The control function block 36 provides overall control of the system 20.It has the capability of accepting commands from and transfer responsesto the host system 20 connected to the computer interface port 26 and/orthe auxiliary interface and provides the capability of acceptingcommands from and transfer an appropriate response to the manualinterface 34 via the processing control function block 84 and thetransport control function block 90. Upon receipt of a command, thecontrol function block 36 interprets the command and performs thefunctions necessary to execute it. The control function block 36 alsoprovides the capability to enable and disable each computer interfaceport, such as interface port 26. It also provides the capability ofqueuing commands from the host system 20 which it processes the order inwhich the commands were received. It also maintains accumulatedoperational status history data in a nonvolatile memory which may beaccessed for system analysis.

The manual interface 34 will be functionally described in connectionwith FIG. 6 which illustrates the operator visible manual interface thatis physically located on the front of the system 20. The manualinterface 34 contains a manual ready/not ready control switch 100, whichif in the ready mode, permits the system to enable the computerinterface port 26, disable the manual interface controls except for theready/not ready control. If the control switch 100 is in the not readymode, the system 20 disables the computer interface port 26, enables themanual interface controls and accepts all commands across the auxiliaryinterface. The control switch 100 does not require electrical power forits state to be changed. The interface 34 includes a ready statusindicator 102 which indicates whether the system is ready or not ready.Another indicator 104 indicates when a cassette is loaded in the system20. A write protect indicator 106 provides an indication whether thetape cassette is write protected and is on if the cassette is writeprotected. An attention indicator 108 provides an indication if therehas been a failure detected. Additionally, a message display 110 isprovided which has the capability to display a minimum of eightalphanumeric characters which relate to various operating statusconditions and commands. The manual interface 34 also contains a manualunload select control 112 which provides the capability for an operatorto select one of four tape unload positions which are identified byindicators 114, 116, 118 and 120. The BOT indicator 114 signifies anoperating mode in which the cassette will be rewound to the beginning oftape before it is unloaded. The EOT indicator 116 signifies an operatingmode in which the tape is wound to the end of tape before it is ejected.The system zone indicator 118 signifies an operating mode in which thetape is wound to the nearest system zone where it is stopped and thecassette ejected. The immediate eject indicator 120 signifies anoperating mode in which the cassette is ejected without winding the tapeto a predetermined position. Operating the switch 112 will sequenceamong these four possibilities and pressing an eject switch 122 willresult in the cassette being ejected at the appropriate tape positionassociated with the operating mode selected.

System Format Overview

Each tape of a cassette, when utilized in the system, has commonphysical and logical parameters associated with it for performingrecording and reproducing operations in the system. Referring to FIG. 5,the format of the tape is illustrated and it has a transparent leader130 located on each end, and a section at the beginning of the tape thatis identified as a BOT section as shown. To the right of the leftportion 132 of the beginning of tape section is a physical location oftape mark 134 (PBOT) that identifies the beginning of the magneticrecording surface.

After the PBOT location, a beginning of tape zone 136 is established inwhich data relating to format considerations is recorded. After the BOTzone 136, a physical beginning of media mark 138 (PBOM) is establishedwhich identifies the first location in which recording of volume formatinformation 140 is permitted. After the volume format information, abeginning of media mark 142 (BOM) is established which identifies thearea of the tape after which user data can be recorded. Thereafter,files of user data can be recorded, such as at 144 and 146, which cancover a substantial length of tape.

In the lower portion of FIG. 5, there are logical and physicalparameters relating to the end of the tape and they include an end ofmedia mark 148 (EOM), a physical end of media location 150 (PEOM), whichidentifies the location on tape in which recording of user data has tostop. An end of tape section 152 (EOT) is identified and an end of tapezone 154 is used for loading and unloading tape. A physical end of tapelocation 156 (PEOT) identifies the last portion of the magnetic tape.

The tape may have one or more system zones 158 located along the lengthof tape in the cassette and the system zones are provided to enableloading and unloading of the cassette at location other than thebeginning of tape or the end of tape. It should be understood that withthe extremely high data rates that are accomplished by the system, datarecorded on tape may be vulnerable to damage by the threading andunthreading operation of a tape when-it is loaded into the system. Thesystem zones are provided to have a length of tape where user data isnot recorded so that the system can position the tape within thecassette with the system zone spanning the tape path defined by thetransport during loading and unloading. Also, the tape comprises avolume which may be divided into a number of smaller volumes and theseare defined herein as partitions in which recording and reproducing canbe done.

Broadly stated, the use of partitions enables a very long tape to beeffectively divided into a number of recordable areas and recording andreproducing can be accomplished in each of the partitions as desired,and therefore support added recording of information data including userdata within each partition without affecting the recordings that may belocated upstream or downstream of the subject partition. Near the end ofthe tape is an end of media warning indication 160 (EMW) and that ispreceded by an early end of media warning or EEW indication 162. The endof media warning is a predetermined number of double frames prior to theend of media location 148 and are calculated for each partition. The EEWmay be set by the host system 24.

The relationships of the partitions are also shown in FIG. 10 whichillustrates a complete tape having a number of partitions n, and eachpartition has an address that identifies the end of the prior partition(EOP) which is at the interface of the last double frame and thebeginning of the next partition (BOP) which is the next double frame.Each partition will have the EMW and EOM locations identified andpreferably the end of media mark (EOM) indication is the three doubleframes before the end of partition and the EMW warning location ispreferably 10 double frames before the end of the partition.

Also, within each partition, there is the BOM zone 143 which preferablycomprises 25 double frames of information which includes volume formatinformation for the partition as well as synchronizing information forit. The EEW and EMW marks are calculated locations which imposeconstraints on the recording that is being done within a partition, andreadies the system to end any recording being done within thatpartition, since physical blocks cannot be incompletely recorded withina partition and therefore cannot span from one partition to another.

With respect to the format that is used to record information on thetape, and referring to FIG. 7, the tape shown has a helical recordingarea 170 of tracks that extend across the tape diagonally to its lengthin which the rotatable heads record and reproduce information dataincluding user data and system format data as will be described. Alsothere are three recording areas, each having a track extendinglongitudinally along the length of the tape. These include a logicaladdress track 172, a physical address track 174, and a servo track 176.The logical address track is for recording address data relating to thephysical blocks and user data blocks that are recorded on tape. Thephysical address track 174 is for recording data which identifies thedouble frames that are recorded in the helical area as well as otherinformation, but it does not identify the logical information orinformation relating to the identity of the data that is recorded in thehelical area. It can be analogized to a tape counter function, albeit anextremely sophisticated one. The servo track 176 is for recording servoinformation for use by the tape servo system for controlling therelative head to tape position and velocity, and provides sophisticateddigitally recorded servo marks as well as information which identifiesthe start of a double frame and of specific subportions of each doubleframe.

System Zones

The system 20 provides maximum data integrity by using system zoneswhich are fixed length areas along the length of tape, preferablyoccurring at regular intervals which are reserved for system use. Byutilizing these zones, as previously described, the system can supportthe implementation of nonbeginning of tape loading and unloading andavoidance of user data areas during the threading and unthreading of thetape that occurs during the loading and unloading operations. Suchthreading and unthreading of tape around a helical scanner has thepotential for damaging a recorded area, either by stretching or bypoorly controlled contact with the rotating heads of the scanner. Sincetape deformations can be temporary, the potential exists for datarecorded over an area soon after an unthread operation to subsequentlybecome unreadable when the tape returns to shape.

Such fixed system zones are dedicated to such mechanical operations andhelical recording is not performed within the zones, but thelongitudinal tracks in these zones are recorded. It is preferred thatthe system support the location of the system zones at fixed locationsfor each size of cassette, so that upon reuse of a cassette, which mayoccur after bulk degaussing, for example, the system zones are at thesame longitudinal locations along the tape during subsequent use of thecassette. While the smallest commercial tape length may have no systemzones, the larger cassettes with their increased length tape capacitiesmay have several zones. It is preferred that a small tape cassette mayhave three recording sections, i.e., two interior system zones, a mediumcassette have six recording sections and a large cassette have 12recording sections separated by 11 system zones. It is contemplated thateach of the zones be approximately one meter in length, but which canalso vary depending upon the length of the tape in the cassette.

In the system zone, there are two subzones, one of which is the loadoperation zone (LOZ) and the other of which is the volume formatinformation zone (VFI). In the load operation zone there is no recordingperformed in the helical recording area by the helical scanner, but thelongitudinal tracks are recorded in this zone. The VFI zone is identicalto that shown after the beginning of tape (BOT) zone which comprises the25 double frames of VFI information. The reasons that the VFI zone islocated downstream or in the forward direction of the load operationzone in each system zone is that if a cassette is loaded on the system,at a location other than the beginning of tape, then the tape can bemoved forwardly to obtain the VFI information which tells the system ofthe format of the tape for operational purposes.

The format allows for some speed variation, i.e., on the order of 0.2%,and the speed between different physical systems may vary significantlyfor the reason that the speed is a function of the amount of tape in acassette. For small tapes, it is recommended that the load operationzone consist of approximately 225 double frames. A medium cassettepreferably has load operation zones consisting of approximately 411double frames and a large cassette preferably has load operation zonesof approximately 754 double frames. Also the last two double frames inthe VFI zone of a system zone can be converted to amble double framesfor the purpose of providing a gapped append type of recording, ifdesired.

If a VFI volume format table is not recorded by the system, then theentire 25 double frames of the VFI zone are recorded as amble doubleframes. The subarea data of such amber double frame is recorded onpreferably every helical track and it contains VFI data containing thesame type of information recorded in the VFI table. If the VFT table isrecorded, the 25 double frames are recorded as physical block doubleframes, but the last two can be converted to amble double frames. Theinformation in the VFT is repeated 128 times in each physical block ofthe 23 or 25 double frames in the VFI zone.

System Partitions

The beginning of partition is a location on tape that denotes thephysical beginning of a partition while the BOM is a recorded entitythat identifies the logical beginning of a partition in a volume. A BOMwill consist of 25 consecutive recorded BOM double frames. The firsttrack of the first BOM double frame of a BOM is the BOP.

The partitions can be defined in terms of two groups of partitions. Eachgroup can have a different size and a different count of partitions. Onegroup can have several small partitions followed by the second grouphaving several large partitions or visa versa, and these two groups arethen replicated throughout the tape volume. The partition sizes areeffectively transparent to a host system because the host system merelyaccesses partitions by partition number and is not concerned with thesize of the individual partitions that it accesses. The partitioninformation is located in subblock 1 of the subarea data illustrated inFIG. 22.

There are two different size partitions that are supported by the systemand are defined as partition group A and partition group B with eachgroup having a predetermined size and a count of the number ofpartitions. A tape is partitioned by recording the partitions by firstestablishing the number of partitions specified in group A followed bythose in group B and thereafter group A and group B are alternated untilthe volume of the tape has been fully partitioned. In the event that avolume partition table is utilized and if it cannot be represented inthe form of a VFT table, then the fields in the volume formatinformation of subblock 1 of the subarea data is set to zero.

Helical Subarea Matrix

In accordance with an important aspect of the present system, thediagonal or helical tracks that are recorded in the helical area 170 ofthe tape include physical blocks of user data, and also include systemformat information which is used by the system to perform necessaryoperations. While it is preferred that the system format information beincluded on every helical track of each double frame, it is possible towrite the information on some lesser number of tracks. Since eachphysical block is written as a double frame of data on 32 helicaltracks, the system format information relating to the physical block andto the system is recorded 32 times for each double frame.

While the information for each helical track changes as will becomeevident, the system format information is always present. It should alsobe understood that the system format information is encoded with theuser data recorded on the helical tracks so that it is interleaved withthe user data along the entire length of each of the tracks. However,the system format information comprises a small quantity of informationrelative to the user data that is being recorded.

More particularly, and referring initially to FIGS. 11 and 12, FIG. 11illustrates a matrix of data with each small square representing a byteof data. The data of each track comprises user data in the area as shownand occupies the bulk of the total data that is written on a track. Thematrix also includes a subarea as shown, in which 192 bytes of systemformat information is contained. The remainder of the data is C1 typeerror correction code data and also C2 type error correction data. TheC1 and C2 areas are illustrative and these areas comprise a largernumber of bytes than are actually shown in FIG. 11. The user data isencoded with C3 type error correction code.

During operation, the data is written into a buffer (in theencode/decode function block 74 of FIG. 4) as previously described, andthe data from the buffer is read out for recording on tape. The data inthe subarea, while written into the buffer as a stream of data, will beread out of the buffer and written onto tape incrementally, whichnecessarily spaces on tape each byte of information from its adjacentbyte in the subarea when it is recorded. As previously described, theerror correction code is more comprehensively described in theabove-referenced application entitled "Triple Orthogonally InterleavedError Correction System", by Kirk Handley, Donald S. Rhines and WilliamMcCoy.

The subarea of 192 bytes is organized as shown in FIG. 12 which includessix subblocks 0 through 5, with each subblock having 32 bytes of data.Subblocks 0, 2 and 4 contain the identical information and thatinformation is shown in FIG. 21 which includes data relating to thephysical block being written. Subblock number 1 of the subarea containsvolume format information and the content of this information isillustrated in FIG. 22. Subblock 3 is reserved for future use and thesystem currently does not use any information in these 32 bytes.Subblock 5 contains a time stamp indicating in real time when arecording is made, as well as vendor information.

With respect to the data recorded in subblock 0, 2 and 4 shown in FIG.21, it comprises physical block information relating to the physicalblock being recorded in its associated helical track. It includes theformat identifier (FID) in byte number 0 which is an 8-bit byte, thecontents of which are shown in FIG. 23. As is shown in FIG. 23, thisbyte specifies whether the tape has been preformatted. If pre-formatted,it would have the physical address track recorded with relevantinformation and also the servo track. Bit 5 of the FID byte specifieswhether system zones have been enabled, bit 4 indicates whether apartition table is provided or not. In this regard, a partition table,as will be described, includes information relating to the location ofthe partitions and system zones that have been defined for the tape.While it is possible to partition the tape with two sizes of partitionsthat are defined in terms of the number of partitions and the size ofpartitions of each type, the use of a partition table which is locatedat the beginning of tape and immediately after each system zone, enablesmany different sizes of partitions and system zones with their locationbeing specified are possible.

Returning to FIG. 21, the physical block information also includesinformation in byte number 1 which identifies the zone type and itcontains four bits which identify whether the zone is an informationzone, a volume format information zone, a load operation zone, orreserved zone. If the zone type indicates that the zone is aninformation zone, then the other bits of byte 1, in conjunction withbyte 2, identify the partition. If it is not an information zone, thenthese bits define the type of physical block double frame that iscontained in partition group B.

Byte 2, in conjunction with byte 1, identifies the partition if the zoneis an information zone, otherwise it identifies the system zone. Bytes3-6 specify the file section number of the user data which is beingrecorded, and bytes numbers 6-11 specify the first data block number inthe helical track being recorded or if a stream of data such as from aninstrumentation recorder is being recorded, and which have no logicaldata block boundaries, then the byte number is recorded in these fields.Byte 12 utilizes bits to specify whether data blocks as opposed to bytesof data are being recorded, whether a data block check sum is enabled (acheck sum is not useful for recording bytes of data from aninstrumentation application).

Byte 12 also contains an EMW flag, which is set when a double framebeing recorded is within ten double frames of the end of a partition onthe tape. Byte 12 bits 4-0 and bytes 13 and 14 also has data definingthe size of the user data blocks being recorded. Bytes 15, 16 and 17specify the total count of total user data bytes in a physical blockdouble frame. If recording of data blocks is being done, so that datablock check sum bytes are included, the total byte count includes allthe data block check sum bytes in its count. The range of this field isfrom 1 to 1,199,840.

Byte 18 comprises a physical block sequence tag that will be hereinafterdescribed. Byte number 19 enables rewriting of physical blocks upon lackof verification of accuracy of the physical block being recorded, aswell as a rewrite count that is permitted and which is remaining, withthe count preferably having a maximum of 20. Bytes 20 through 25 specifythe cumulative data block/byte number which represents the total countof all user data blocks that have been recorded in the partition.

Bytes 26 through 28 specify the absolute double frame number which isalso recorded on the physical address track and this number identifieseach double frame regardless of its type or the information that wascontained in it. Four bits of byte 29 specifies the type of doubleframe, of which there are presently only one.

The other four bits of byte 29 specify the helical track type, which isan identification of the seven different types of double frames thathave been previously described. These are shown in FIG. 20 and includethe various end of recording types of double frames, the beginning ofmedia double frame, as well as demark, amble and data double frames. Thefinal byte 31 comprises seven bits of subarea subblock cyclic redundancycheck (CRC) information which is inverted.

Volume Format Information

The data contained in the 32 bytes of subarea subblock 1 relate tovolume format information data and comprises data relating to partitionsand system zones. This information is included in the subarea that isrecorded on each helical track so it is recorded in the helicalrecording area. Moreover, at the physical beginning of media and aftereach load operating zone, there is a volume format information zonewhich contains this information, and possibly a volume format table aspreviously described.

Turning now to FIG. 22 which illustrates the volume format informationthat is contained in subblock 1 of the subarea data of each helicaltrack, byte number 0 has two bits dedicated to a partition layout optionwhich specifies how data is to be written in a partition when a systemzone is encountered. In this regard, it should be understood that asystem zone may occur in the middle of a partition and these two bitsspecify whether the portion of the partitions before and after thesystem zones are to be treated. It should be understood that adiscontinuity in the partition would result in an interruption duringdata transfer, but the partition size or capacity is neither increasedor decreased by a system zone being present. If a pack option is chosen,then a second partition is always abutted against a first partition. Ifthe pack option is disabled, the second bit specifies a stretch or awaste option. The stretch option extends the prior partition to thebeginning of the system zone and begins a new partition at the oppositeside of the system zone. This is done during recording or during apre-formatting operation. The second bit may also specify a waste optionin which the tape after the end of the previous partition and before thesystem zone is not used to record information and that partition isbegun on the other side of the system zone.

The other six bits of byte 0 and byte 1 specify the system zone size andbytes 2, 3 and 4 specify the system zone spacing. In the event that avolume format table is not used, the system permits two sizes ofpartitions which are defined as group A and group B partitions and bytes5-7 specify the size of partition group A partitions with byte number 8specifying the count of them. Bytes 9 through 11 specify the group Bsize with byte 12 specifying the count of group B partitions.

Bytes 13-18 are used for vender identifier and provides a record whichenables a subsequent system which reproduces recorded tapes from anothersystem to identify the prior system where the recording was done in theevent that there is a problem with the recording that could warrantrepair and/or correction. Bytes 19-21 specify the last double framenumber that is the double frame at the physical end of media (PEOM) andshould not be used for recording. Byte 22 specifies the last validsystem zone. Byte 23 and four bits of byte 24 identify the last validpartition with the other four bits of byte 24 specifying the partitiongroup A physical block double frame type. Bytes 25 through 30 specifythe volume identifier data and byte 31 includes subarea subblock 1 CRCinverted data.

Volume Format Table

The system 20 has the capability of providing a volume format table thatis located at the beginning of tape and near the end of each systemzone, with the volume format table providing data that specifies thelocation of each partition and system zone that is present in the volumeor tape cassette. An advantage of the use of the volume format table isthat partitions and system zones of virtually any size within theconstraints of the system can be established, and one is not limited tothe use of the predetermined size of partitions that is supported by thegroup A and group B partitions in the volume format information insubblock 1 of the subarea data. This adds to the flexibility and use ofthe system and does not impose constraints on the size and location ofpartitions and system zones that may be desired by a host system. Theinclusion of the volume partition table after each system zone and atthe beginning of tape permits the tape cassette to be loaded at anysystem zone and the system can immediately obtain the partitioninformation for the entire tape.

The table is structured as shown in FIG. 24. The table is a fixed size,preferably 9,004 bytes that can contain up to 1,125 entries. It hasthree parts as shown in FIG. 24, the first part of which specifies thenumber of valid table entries in the table. The second part comprises9,000 bytes and is used to contain up to 1,125 eight byte table entries.If less than 1,125 table entries are used, the unused space ispreferably filled with zeros. A third part of the table comprises twobytes in which a partition table check sum is provided and it is derivedby adding the 9,002 bytes on a byte-by-byte basis and then taking theone's complement of the sum and keeping the least significant 16 bits asthe check sum.

The table enables the volume to be divided up to 1,124 nonoverlappingbut contiguous tape sections and for each table entry there is one eightbyte section. The order of the section entries in the table areestablished based on the location of each section relative to thebeginning of tape. For example, the section entry for the first VFI zoneshall always be the first entry of the table and shall occupy bytes 2through bytes 9 of the table. Also, each table has one end of volumeentry following the last tape section entry. With respect to the sectionentries, they identify the type of a tape section, its beginninglocation and an associated identifier if applicable.

The definition for section entries is set forth in FIG. 25 and islargely self-explanatory. The starting double frame number for thesection specifies the double frame identification number of the firstdouble frame of that section. The physical block double frame typespecific the type of physical block double frame that may be used inthat section. The partition/system zone identifier located in four bitsof byte number 4 and byte 5 comprises a 12-bit field that is used tosequentially number the partitions for the system zones in a volume.Four bits of byte 6 specifies the table entry type which includes eitherthe beginning of the-first VFI zone, the beginning of a system zone, thebeginning of a partition or the continuation of a previous partition.

With respect to the end of volume entry, i.e., the last entry in thetable, it is shown in FIG. 26 and includes data relating to the lastvalid system zone identifier, the last double frame number of thevolume, the last valid partition number, and a portion of a byte whichspecifies that it is the end of volume entry.

Types Of Double Frames

In accordance with an important aspect of the system disclosed herein,recording and reproducing of user data blocks that are formatted intodouble frames of information are recorded on 32 helical tracks, as hasbeen previously described. The system 20 operates to perform recordingand reproducing of double frames with a major consideration residing inthe identification of each double frame being of a particular type.

As previously described, there are seven types of double frames whichare set forth in FIG. 20. The type of double frame is specified in byte29 of the physical block information (see FIG. 21) which is recorded insubblocks 0, 2 and 4 of the subarea section of the system format datarecorded in each helical track of each double frame. Thus, each recordedphysical block or double frame of data is a specified type of doubleframe. In addition to the HTTY field being uniquely specified for eachtype, there are other fields in each type of double frame that aredifferent in various ones of the types.

In FIG. 21, the various fields of data are set forth and for a datatrack type double frame, the fields set forth in FIG. 21 are allapplicable. A data track double frame has its HTTY field set to 0101 andthe double frame is used to record user information as well as systemformat information concerning a recording. When a recording is to bemade in any partition, a number of beginning of media double frames (BOMDF) are recorded to permit the system to become synchronized and it ispreferred that approximately two seconds of BOM DF's be recorded and forthis reason 25 BOM double frames are recorded in this area.

When the recording is begun, under certain conditions such as an appendrecording where additional double frames are recorded on an existingrecording at the end of prior recorded data, an amble double frame willbe written. All of the data written in the helical tracks except for thesubarea data and the error correction code data is the fill pattern andno user data is recorded in an amble track.

In accordance with another important aspect of the amble double frame isthe fact that when amble double frames are recorded, two double framesare recorded, with the first having the unique characteristic that therecording heads of the scanner are not energized during the first 16tracks. This results in a gap between the prior recorded double frameand the first amble double frame that is approximately 1/2 of the widthof the double frame. The gap is useful in compensating for any trackingmisalignment that may exist with the system recording the new data andthe prior recorded double frame. If the prior recording was done inanother machine, the tolerances may be different between that machineand the system in which the present tape cassette is located and theplacement of the gap will preclude the new recording from possiblydestroying some of the latter tracks of the last double frame of theprior recording. The recorded amble double frame provides an area of newrecording that may be needed to obtain synchronization for recoveringthe subsequent data of the new recording. As will be discussedhereinafter, the present system distinguishes between recordings thatwere done possibly on another machine and the present system and if theprior recording was done on the same machine during the same tape load,it is unnecessary to perform a gapped append type of recording and ambleframes may therefore not be required. If the last 16 or all of the 32tracks in a double frame are of the amble track type, the double frameis an amble double frame.

The recording format of the system generally involves the tape beingmoved in the forward direction with the scanner heads recording helicaltracks successively along the tape and if double frames that arerecorded are then detected to be inaccurate, i.e., the double framefails to meet the verification criteria, the double frame will bere-recorded downstream. This is in contrast to stopping the tape,returning it to the location where the double frame was not accuratelyrecorded and re-recording over the double frame that proved to beinaccurate.

In fact, the system records physical blocks, and maintains the datarecorded in those double frames in the system buffer until the readheads on the scanner read the recorded track and the read data is thenanalyzed to determine if it is accurate or not. If it is detected to beinaccurate, the system again records the double frame if it is detectedearly enough, or a prior double frame in addition to the double framecurrently being written are again recorded if the prior double frame wasinaccurate and such inaccuracy was detected later. If the prior doubleframe was detected to be inaccurate, the current double frame beingrecorded will be converted to a demark double frame wherein at least thelast 12 helical tracks are provided with the demark designation whichhas its HTTY field set to "1011". As will be described hereinafter, oncea data double frame is converted to a demark double frame, the doubleframe and the prior double frame are rewritten according to the originalsequence.

The system also utilizes end of recording to provide a mark that arecording operation has ended. End of recording consists of two doubleframes of identical types and there are three types of end of recordingdouble frames (an EOR, an EOR/T and an EOR/E double frame). The EOR/Tdouble frame represents an entity used to identify the current end ofrecording of a partition. If there are more than one EOR double frame ina partition due to overwrite recording on already recorded tape, the EORthat is closest to the beginning of media of the partition is consideredto be the valid one.

The normal EOR consists of two consecutive recorded EOR double frames.The file system number FSN fields of the first EOR double frame have thesame values as the FSN of the last physical block or double frame. TheFDBN of both EOR/T double frames will be one larger than the lastphysical block number of the last physical block or equal to the FDBN ifthe last physical block is an empty physical block. All of the FSNfields of the second EOR double frame shall be equal to the sum of theFSN of the last file section and the additional tape marks countsrecorded. The FDBN fields of the second EOR double frame shall all beset to zeros. If there is an append recording, the EOR double frames ofany of the three types will be overwritten by the new recording and thenew recording will then end with two EOR double frames of one of thethree types and may be at a different location.

In addition to the normal EOR double frame, an EOR/T or temporary end ofrecording can be written and it consists of two consecutively recordedEOR/T double frames located in each track. The EOR/T double frames areautomatically recorded by the system 20 when the record operation istemporarily stopped due to lack of data from the internal buffer. All ofthe FSN fields of both EOR/T double frames shall have the same FSN valueof the last recorded physical block. The FDBN of both EOR/T doubleframes will be one larger than the last physical block number of thelast physical block or equal to the FDBN if the last physical block isan empty physical block.

The last EOR double frame type is an EOR/E or error end of recording andit consists of two consecutively recorded EOR/E double frames. This EORis recorded by the system to indicate a detection of recording failureand the recording operation is terminated by the recorder. It is in theinherent operation of the system that there will always be one demarkdouble frame located between the failed physical block double frame andthe EOR/E double frame. All of the FSN and FDBN fields of both EOR/Edouble frames shall be set to the FSN and FDBN value of the physicalblock that was the cause of the recording failure. Due to the recordingof EOR double frames, the gapped append using amble double frames willnot produce an unrecorded gap on tape.

Recording and Logical Overrecording Double Frames

The system records data blocks in a partition by appending to the BOM ofthe partition if physical blocks or file marks are to be recorded. For apartition which already contains recorded physical blocks, writing canstart in the recorded area and this is called an overwrite oroverrecording. Overrecording will invalidate all existing recordingdownstream or behind the starting point of the overwrite.

Of the seven types of double frames that have been hereinbeforedescribed, only the physical block double frame and the EOR doubleframes are recorded under commands. The other five types of doubleframes are recorded automatically by the system, either during theformatting process, e.g., BOM double frames, or when certain situationsarise as will be described.

A physical block will be recorded in one or more physical block doubleframes that are interspersed with demark double frames and/or ambledouble frames if rewrite or gap append has occurred, respectively.Demark double frames and amble double frames will have the identicalPTID, FSN and FDBN values with the physical block double frames beingrecorded. If the recording is not ended with an EOR/E, the last physicalblock double frame is considered as containing a valid physical block. Afile mark is recorded implicitly as an increment of the file sectionnumber (FSN) or explicitly as a normal EOR. The explicit file markrecording will be converted to the implicit file marks when appendrecording is performed.

The recording format may be more readily understood while referring toFIG. 9, FIG. 9(a) of which depicts several double frames 1-5 which arerecorded without failure and the end of the recording therefore has twoEOR double frames which end the recording, those being shown inlocations 6 and 7.

If there are additional double frames that are to be added to therecording shown in FIG. 9(a), i.e., an append recording, then as shownin FIG. 9(b), the EOR double frames at locations 6 and 7 will beoverwritten with physical block double frames 6 and 7, and when thatrecording has successfully ended, additional EOR double frames arerecorded at locations 8 and 9 to identify the end of that recording.

The append recording shown in FIG. 9(b) requires that the double frames1 through 5 as well as 6 and 7 are recorded by the same system and thatthe physical tolerances result in the inclination of the helical tracksbe the same in one double frame as those of an adjacent double frame.Therefore, there is little chance that an append recording would destroytracks of the prior double frame. In this case the first track of doubleframe 6 would not overwrite any of the ending tracks of the double frame5.

If the failure of write verification of a physical block double frame isdetected before the beginning of the next double frame recording and ifno boundary condition exists, the same physical block is recorded at thenext double frame. Referring to FIG. 9(c), and particularly during thewriting of the double frame 5, if the write verification fails duringthe early portion of the writing of the double frame, i.e., earlydetection. the same double frame 5 will be rewritten at the next doubleframe, in this case at location 6.

In the event there is a late detection of write verification which isnot verified until the system is recording the following double frame 6,the double frame 5 will have been recorded without any indication thatit is defective. However, the write verification failure for thephysical block 5 written at location 5 will cause the physical block 6at location 6 to be demarked and the buffer information containing thephysical blocks 5 and 6 will be used to rewrite physical block 5 inlocation 7 and physical block 6 in location 8. Because of theabove-described manner in which write verification is accomplished, uponrecovery or reproducing of the physical blocks, it is always necessaryto examine two successive physical blocks after a subject physical blockto confirm that the subject physical block is valid.

As previously mentioned, the system 20 supports a gapped append, whichis illustrated in FIG. 9(e). The gap append is used as a precautionarymethod by providing a gap between old and new recording to prevent thenew recording from damaging an existing recording. Without the gap, thenew recording if done by a recorder with different track curvature, mayoverlap onto some track of the old recording and damage the oldrecording. The gap is provided by appending two amble double frames tothe old recording before recording physical blocks or an EOR doubleframe. The first of the two amble double frames will have its last 16tracks recorded new and the first 16 tracks will be left intact withwhatever was recorded previously. The previously recorded 16 tracksbecome the buffer zone or gap between the old and the new recording.

The system 20 can overwrite prior recordings in one of two ways, i.e., afull or a partial overwrite which is dependent upon whether the firstdata block to be overwritten is at the beginning of a physical blockdouble frame or not. If the first data block to be overwritten is thefirst data block of the physical block containing it, the whole physicalblock will be overwritten in the manner described in connection with9(b).

However, if the first data block to be overwritten is not the first datablock of the physical block containing it, then that physical block willbe preserved, and the overwrite will start at the next double frame witha physical block having that prescribed data block as its first datablock. This is diagrammatically illustrated in FIG. 9(f) wherein adouble frame "n" contains a file section number "m" and a first datablock number 10 and a last data block number 21 the latter of which iscalculated by the system. If the host system commands a rewriting ofdata blocks beginning with data block 15, it should be appreciated thatdata block 15 through 21 would have been recorded in double frame "n".Therefore double frame "n" is retained since it contains presumablyvalid data block numbers 10 through 14 and double frame "n+1" isrecorded beginning with the first data block number 15 and it will havedata blocks 15 through 35 within it.

Nonrecording Failure Detection

The system disclosed herein has the capability of recording data on atape that has been previously recorded without the necessity ofdegaussing the tape. Because of this capability, it is possible, if notexpected that many locations along a tape will have data written overpreviously recorded data.

Since the double frames begin at predetermined locations along the tape,previously recorded double frames may otherwise appear to be part of alater recording, if the later recording did not actually record newdata. Stated in other words, if there is a nonrecording failure thatoccurs during recording of data and the nonrecording failure occurs whenan old recording is intended to be overwritten, then there will be areason tape where the new data will not be recorded. If this is notdetected, then during reproducing, the system will be reading the oldpre-recorded data that is not valid. Such a nonrecording failure can becaused by various problems, including the failure of a recordingchannel, the failure of a recording head or the temporary logging of arecording head.

The system has the capability of determining whether a nonrecordingfailure has occurred by virtue of data that is recorded in the subareamatrix, and particularly the physical block information field of thesubarea matrix data. Referring to FIG. 21, byte 30 includes cyclicredundancy check data which is generated for the entire physical blockinformation subgroup (see FIGS. 11 and 12) and it will have a uniquecontent by virtue of the inclusion in the recorded physical blockinformation of the absolute double frame number (ADFN) and thecumulative data block/byte number (CDBN). Since both of these numbersincrement during the recording of the user data, the generated CRC datawill be unique for each track.

As has been previously described, the system has a read-while-writecapability wherein a read head reads the data that has just beenrecorded during a recording operation. The read heads on the scannerspreferably read the adjacent track that has just been recorded.

The data that is recorded is also stored in a buffer as has beenpreviously described, for the purpose of performing an accuracyverification, so the cyclic redundancy check data is necessarily presentin the buffer. The CRC data recovered during the read-while-writeoperation can be compared with the CRC data written in the buffer, andif the comparison does not reveal an identical value, then the systemdetermines that a nonrecording failure has occurred.

Alternatively, a time stamp located in subblock 5 of the subarea data(see FIG. 12) is used to record the specific time in which a doubleframe was recorded, with the time including the portion of a second, theminute, hour and date in which the double frame was recorded. In thisregard, the system includes a 250 Hz internal clock which provides suchinformation for 100 years starting with the year 1990. Upon recoveryduring reproducing, the specific time in which the double frame wasrecorded can be compared with specific times of that double frame thatis contained in the buffer, and if the time is not identical, the systemwill generate data indicating a nonrecording failure.

Still another alternative is to use the CDBN of each physical block forthe check. Since the CDBN will be different for each physical blockwithin a partition, it provides the required uniqueness in detecting anon-recording failure.

The Servo Track

The digital servo track shown in FIGS. 7 and 8 includes data that isshown in FIGS. 17 and 18, which data comprises four different fields,each of which comprises a 12 bit field and which are shown in FIGS.18(a), 18(b), 18(c) and 18(d). A field is written or recorded on theservo track for each track pair, so that each double frame will have 16fields written along the servo track. The fields are selectively writtenon the servo track depending upon the location of each track pair, andthe locations are shown in FIG. 19. More particularly, the field of FIG.18(a) is written in all but the 0 and 8th track pair, the field of FIG.18(b) is written at the 8th track pair, the fields of FIGS. 18(c) and18(d) are alternately written at the track pair 0.

Each of the fields, when reproduced, appear to be identical to a servoreproducing head when the tape is moved in either the forward orrearward directions. The fields comprise data which in the first half ofthe field are reversed in polarity relative to the second half of thefield. Also, the location of the transitions from the left in the leadservo mark identifier are the same as the location of the transitionsfrom the right in the trail servo mark identifier.

As shown in FIG. 18, each of the four fields includes a lead servo markidentifier and a trail servo mark identifier, with an ANSI sync wordpositioned between the lead and trail servo mark identifiers. The ANSIsync word is also used to determine the direction of tape motion duringreproducing.

With respect to the servo track, the structure of it is such that it hasthe same recovery time regardless of the direction of searching and thetransition in the middle of the ANSI sync word is the digital equivalentto the peak of a spike that normally occurs in analog servo tracks. Asis shown in FIG. 19, there is one servo pulse for each pair of tracks.The leading and trailing servo mark identifier sections of the 12-bitfield also have an error correction aspect in that for each type of12-bit field which identifies either a single track pair, a singleframe, a double frame or a quad pair, there are two bits in eachidentifier that are different from bits of another type of identifier,which aids in reliable recovery of data which indicates the type of pairthat is to be identified. It is therefore less error prone. Prestripingthe tape means only the servo track has been prerecorded.

Longitudinal Address Tracks (PAT and LAT)

All of the information that is recorded on the longitudinal tracks,including the physical address track and the logical address track,which relate to the physical blocks that are recorded is identifiednominally and monotonically. Therefore, all such longitudinal trackinformation is useful in accomplishing searching. The main differencebetween the logical and physical address tracks is that every time thereis an over recording or rewrite, for example, the logical trackinformation can change while the physical address track relates to thephysical layout of the tape regardless of the logical content that isrecorded in the helical recording area.

Since only the logical address track is needed for recording datarelated to the logical content of data, the servo and PAT tracks are notvariant with the helically recorded data, and they can be used topreformat a tape. When a tape is formatted with multiple partitions, theboundary of partitions can be easily positioned to. Thus, the tape canbe preformatted by only recording both the servo track and the physicaladdress track. The tape can be merely prestriped which means that onlythe servo track is pre-recorded which provides some servo consistencyupon interchange with other transports. However, the present systemfully supports writing all of the longitudinal tracks during a recordingoperation and no pre-recorded information is necessary for the system.

The longitudinal tracks include the logical address track 172 and thephysical address track 174 shown in FIG. 7 and they are written withtrack segments as shown in FIG. 8. Each logical address track segment(LATS) and physical address track segment (PATS) has a format as shownin FIG. 13 that comprises a front padding portion of 2.5 bytes, a rearpadding portion of 2.5 bytes, an ANSI Sync Word of 0.5 byte, andinverted ANSI Sync Word of 0.5 byte and a segment information portion of18 bytes. The front padding portion comprises ten repetitions of a "10"pattern as is shown in FIG. 16, while the rear padding portion comprisesten repetitions of a "01" pattern as shown in FIG. 17. The use of theANSI sync word in the logical address track, as well as the physicaladdress track and the servo track enables the synchronization ofinformation from each of these tracks to be accomplished.

The inverting of the ANSI sync word near the rear padding portion ofeach of the longitudinal address track segments allows detection ofencountering a segment during movement in the reverse direction to bethe same as in the forward direction.

The front and rear padding enable the system to become synchronized sothat the information relating to each segment can be recovered and alsothe front padding provides a gap of space which may be partiallyoverwritten if during an append recording, and the padding will isolateeach segment information portion so that it will not be destroyed.

With respect to the physical address track segment information, there isonly one type of segment information being recorded, and the informationrecorded in it is shown in FIG. 15. As is evident from the informationshown in FIG. 15, the data specifies physical parameters of the tape,including the absolute double frame number (ADFN), the volume identifier(VLID), system zone size (SZSZ) and system zone spacing (SZSP), all ofwhich relate to locations on the tape regardless of the content of thedata recorded in the helical tracks.

With respect to the logical address track segment (LATS) information,there are four different types of segment information written dependingupon the content of the data being recorded on the helical tracks. Asshown in FIG. 14, type II, type III or no LATS segment information iswritten in the beginning of tape zone and type II segment information iswritten in all the volume format information zones. Type I, III or EORsegment information is used in the information zones when physical blockdouble frames are being recorded. Type I is recorded when physicalblock, amble or demark double frames are being recorded. Type III isonly used for initialization purposes. Type II information is alsowritten in all the load operating zones (LOZ) of a system zone, and theend of tape zone (EOT) contains type III or no segment information. Theinformation for each of the types is shown in the various columns ofFIG. 15.

The end of recording (EOR) type of segment information as shown in FIG.15, comprises 36 ANSI sync words which are important during searchingand enables high speed searching to be performed and the information canbe obtained simply using word detecting circuitry without involvement ofdecoding and other, software and quickly identifies an end of recordingduring the searching process. This pattern is only recorded on the LATsegment associated with the second double frame of an EOR of any of thethree EOR types. An existing EOR LATS will be overwritten by any appendoperation and be replaced by a new EOR LATS written probably downstream.The reason for the overwrite is to leave only one valid EOR LATS in apartition.

Physical Block Sequence Tag

The system uses a physical block sequence tag to sequentially numbereach physical block within a partition during recording and thissequence tag enables the system to determine during recovery whetherphysical blocks have been lost and also how many have been lost.

Such information is necessary because of the partial or logicaloverwrite capability of the system. Because of the manner in which theFSN and FDBN numbers are used to support partial rewriting of datablocks in subsequent double frames and the fact that when such partialoverwrites are performed, the subsequently recorded physical blockcontaining the data that is overwritten is given the same file sectionnumber FSN and a FDBN that duplicates the data blocks in the priorphysical block, then these two items of data do not necessarily indicatewhether a physical block has been lost. It is for this reason that thephysical block sequence tag is used to consecutively number differentphysical blocks during recording.

While the sequence tag value is set to sequence for each physical blockthat is written, it is given the same sequence tag number as theprevious physical block if it is a complete overwrite or rewrite.Similarly, those physical block double frames will also carry the samePTID, FSN and FDBN values.

Partition Access Bookkeeping

The system 20 supports a record keeping journal of recording, searchingand reading activities that are performed during a current load of acassette, and the information is stored in a memory. As part of thepartition access bookkeeping, the first time that a recording is done ineach partition of a tape after it has been loaded and the host hasprovided a location in which recording is to occur, the first recordingof the actual user data in each partition is not done until two ambledouble frames have been recorded, with the first amble double framehaving the first 16 tracks inhibited.

The partition access bookkeeping thereafter keeps track of whether therecording is being performed by the same machine during the same loadand decides whether a sapped append should be performed when the tape isrepositioned to record information at a different location on the tape.The bookkeeping aspect of the system keeps track of every partition ontape. Every time the system relocates the tape to a new partition, agapped append amble double frame is written within the partition and byvirtue of the bookkeeping aspect, thereafter further recording in apartition which has been recorded will determine whether the appendrecording is being added to the new recording or if it was an oldrecording.

If the append is to add further data to the recording in a particularpartition in which recording was done during the present session, then agapped append is not called for. An amble double frame is transparent inthe sense that it will not cause any problem during reproducing orsearching for data to provide the data from the system to the hostsystem.

When a tape is loaded into the system, none of the partitions have beenaccessed so that during a search operation the tape is moved to thebeginning of the partition during an initial search. Once a partitionhas been accessed, then the system keeps track of the highest accessedlocation that has being accessed in that partition. For example, if apartition has been accessed to perform an append recording, then at theend of the append recording where two EOR frames have been written andthe locations thereof are therefore known and their location are writteninto the memory.

Since the location of the end of recording is therefore known within thepartition, then that information can be used to perform a search fromeither the forward or the reverse tape direction, because the systemthen knows where the end of recording is within the partition. Becausedata can be written over prior recordings with the prior recordingshaving end of recording double frames written thereon, the priorrecorded information would not reliably enable accurate searching to bedone because the system would not know, without the partition accessinformation, whether another end of recording double frame would havebeen written previously at a location nearer the beginning of thepartition. If the current target is before the highest accessed locationkept in the bookkeeping record for the partition, reverse searchingwould also be allowed, since the highest accessed location cannot bebeyond the EOR even if its location is not known.

Also, if during a prior search, the highest accessed location before anend of recording double frame was encountered and therefore the end ofrecording location was not determined, during a reverse search, if thecurrent target is after the highest access location, the bookkeepinginformation is used to locate the tape at the address and the search isthen done in a forward direction to find the target. This is necessarybecause the system would not know where the valid end of recordingoccurred. The information that is stored in the memory includes thehighest accessed address in each partition, including the file sectionnumber (FSN) in each partition, the data block number (DBN) and thecumulative data block number (CDBN).

Thus, the bookkeeping capability may considerably shorten the timerequired to perform the search. Therefore, from the above it should beappreciated that the information that is most relevant is the valid endof recording aspect and if access to the partition has been done inorder to read information from the partition, then the highest readlocation is necessary to perform reliable searching. If the fact that anappend recording has been performed is known, then the searching can bedone in either direction with a single frame of information.

Longitudinal Searching

With respect to longitudinal searching that is done by the system, itsearches in one of two search modes, one of which is a logical searchmode and the other an absolute search mode. When in the absolute searchmode, the ADFN or absolute double frame number is searched, and it islocated on the physical address track. Since during loading, the systemknows where on tape it is as soon as it begins to read information fromthe physical address track and because the absolute double frame numberis a monotonically increasing value from double frame to double frame,it is relatively easy to transport the tape to the desired location andthe ADFN numbers can be retrieved while searching so effectively it isalmost like a footage counter. This type of searching enables high speedmovement of the tape to be used and may be a tape speed such asapproximately 60 times the normal recording speed.

With respect to the logical search mode of operation, which is to lookfor a particular data block within a recorded partition and in such asearch the system does not know where in a partition the data block islocated. Since the partition in which the data block is located isknown, once the tape is moved so that the partition in which the datablock is located is encountered, the servo slows the tape movement to nogreater than preferably approximately 30 times normal recording speed sothat the logical track information can be recovered.

The search operation continues during movement of the tape until theparameter that is being searched is overshot. When moving in the forwarddirection, the system moves the tape to a partition and the searching isfor a DBN of a file section number. Because of the manner in whichdouble frames are demarked, even if the target file section number andDBN number is located during a forward search, it is necessary to go onto determine if the prior number was a valid physical block, andtherefore it is necessary to overshoot by a number of double frames thatare required in order to confirm that the first target value was in -acta valid double frame. For forward search, the confirmation is achievedwhen there are two consecutive logical address track segments containingFSN and/or FDBN that are larger than the FSN/DBN of the target. During areverse search, the first encountering of a logical address tracksegment containing a FSN and/or FDBN that is equal or less than theFSN/DBN of the target concludes the search.

The system can either search for the file section number (FSN) and theDBN, but not a DBN number alone, because there can be many possible DBNnumbers that match the target number that is being searched. However,for any particular file section number there will be only one DBN numberfor a valid data block and the combination of these two characteristicswould yield the desired data block that is being searched.Alternatively, there is only one unique cumulative data block numberCDBN and a reliable search can be accomplished using this parameterrather than a FSN together with a DBN. The search from a forwarddirection will start at the partition and it will continue until thetarget is reached or an EOR double frame is encountered.

During a logical track search the system iaoves the tape to the area inwhich the data block is believed to be located. However, the systemrequires confirmation of the location by a subsequent search of thehelical tracks done in a helical search to be described, because amongother things, the longitudinal tracks are not encoded with errorcorrection coding and are not totally reliable.

The logical searching is done in conjunction with the partition accessbookkeeping information. To search a given partition, the systemexamines the information known about the partition. If no bookkeepinginformation exists with respect to a partition, the system will accessthe partition at its beginning and then it will begin the searching.

If the partition access bookkeeping provides a known access point from aprior search and read operation, the target data block can be comparedwith that information and if the data block cannot be between thebeginning of the partition and the highest accessed location (not anEOR), the system uses the known access point as a starting point to dothe searching in the forward direction until the target data blocklocation is actually found. Once the logical search on the longitudinaltrack is accomplished and the target is believed to be found, the systemmoves the tape to a pre-roll position that is preferably approximatelytwo seconds worth of tape where the helical search is started and itwill perform its search for the actual data block that is being searchedfor.

If the target data block is between the beginning of the partition andthe highest accessed location, the system can search from the accesspoint to the target in the reverse direction, or from the beginning ofthe partition to the target in the forward direction. Successfullycompletion of a search may provide new access locations for thepartition accessing bookkeeping information.

Helical Searching

With respect to the helical search mode, it is first necessary todetermine that the physical block double frame contains a valid physicalblock, which requires reproducing at least two additional orsubsequently recorded double frames to determine whether a subsequentdouble frame has been designated as a demark double frame. Once thephysical block is determined to be valid, the physical block is searchedto locate the target data block which is being searched for. The end offile is defined as the last physical block with the same FSN. If asuccessive double frame contains a file section number that is greaterthan the prior one, it is defined as the beginning of a new filesection. The beginning of a file has a new file section number with aFDBN number equal to zero.

The mixed mode type of search is an extension of the longitudinal tracksearch and the helical track search whereby a host system has abookkeeping system that it uses and it can command that a search be doneto the system whereby it will request a search be done for a particulardata block and it will also provide an ADFN number that it sends to thesystem 20 and in such event, the system will use the ADFN number toshuttle to the location where the block should be located and once it isthere, then it will perform the above described longitudinal tracksearch in the reverse direction followed by the helical search tocomplete the search.

From the foregoing, it should be understood that an extremely powerfuldata recording and reproducing system has been shown and described whichhas the capability of storing large amounts of data in an extremelyorganized manner. The organization of the format of the system enablesthe system to perform many desirable operational functions, includingreliable searching, recording and recovery of the data.

While various embodiments of the present invention have been shown anddescribed, it should be understood that various alternatives,substitutions and equivalents can be used, and the present inventionshould only be limited by the claims and equivalents thereof.

Various features of the present invention are set forth in the followingclaims.

What is claimed is:
 1. A longitudinal servo track pattern located on an elongated medium having other areas on which information are recorded and reproduced, said servo track pattern adapted to provide signals for a servo system for controlling the position and velocity of the elongated medium relative to a magnetic reproducing head which reads information from the elongated medium, said servo track pattern comprising a plurality of digital mark patterns recorded thereon, each of said digital mark patterns comprising:a leading identifier field of digital bits; a trailing identifier field of digital bits; and a field of digital synchronizing data bits having a transition centrally located between said leading and trailing identifier fields, wherein said transition defines a first half and a second half of said each of said digital mark patterns, said bits of said first half being reversed in polarity relative to said bits of said second half.
 2. A longitudinal servo track pattern as defined in claim 1 wherein said leading identifier field comprises a plurality of bits of digital data, wherein the flux transition directions and locations of said bits in a first direction are predefined.
 3. A longitudinal servo track pattern as defined in claim 2 wherein said trailing identifier field comprises a plurality of bits of digital data, wherein the locations of successive flux transitions in said trailing identifier field from an opposite direction to said first direction are identical to the locations of successive transitions of said leading identifier field transitions in said first direction, the direction of each successive flux transition of said trailing identifier field in said second direction being opposite the direction of each successive flux transition in said leading identifier field from said first direction.
 4. A digitally recorded longitudinal servo track pattern for an elongated magnetic recording medium of the type which has separate recordable and reproducible areas, said servo track pattern being adapted to provide signals for a servo system for controlling the position and velocity of the elongated magnetic recording medium relative to a magnetic reproducing head which reads information from the magnetic recording medium in either a forward or reverse direction of movement, said servo track pattern comprising:a leading identifier field of digital bits; a trailing identifier field of digital bits; and a field of digital synchronizing data bits having a transition centrally located between said leading and trailing identifier fields; said leading identifier field of digital bits being electrically equivalent during reproducing while the medium is moving in a first direction to the trailing identifier field of digital bits while the medium is moving in a direction opposite to said first direction, said digital bits of said leading identifier field further being reversed in polarity relative to said digital bits of said trailing identifier field.
 5. A servo track pattern as defined in claim 4 wherein said leading identifier field comprises a plurality of bits of digital data, wherein the flux transition directions and locations of said bits in a first direction are predefined.
 6. A servo track pattern as defined in claim 5 wherein said trailing identifier field comprises a plurality of bits of digital data, wherein the locations of successive flux transitions in said trailing identifier field from an opposite direction to said first direction are identical to the locations of successive transitions of said leading identifier field transitions in said first direction, the direction of each successive flux transition of said trailing identifier field in said second direction being opposite the direction of each successive flux transition in said leading identifier field from said first direction.
 7. A digital mark pattern for a longitudinal track of a magnetic recording tape of the type which has other areas adapted to have data recorded thereon and reproduced therefrom, the longitudinal track providing servo information for a servo control system that is adapted to control the position and velocity the tape relative to a magnetic reproducing head which reads information from the tape, said mark pattern comprising:a leading servo mark identifier field of digital data; a trailing servo mark identifier field of digital data; and a field of digital synchronizing data having a transition centrally located between said leading and trailing servo mark identifier fields, wherein said transition defines a first half and a second half of said mark pattern, said data of said first half being reversed in polarity relative to said data of said second half.
 8. A digital mark pattern as defined in claim 7 wherein said leading identifier field comprises a plurality of bits of digital data, wherein the flux transition directions and locations of said bits in a first direction are predefined.
 9. A digital mark pattern as defined in claim 8 wherein said trailing identifier field comprises a plurality of bits of digital data, wherein the locations of successive flux transitions in said trailing identifier field from an opposite direction to said first direction are identical to the locations of successive transitions of said leading identifier field transitions in said first direction, the direction of each successive flux transition of said trailing identifier field in said second direction being opposite the direction of each successive flux transition in said leading identifier field from said first direction.
 10. A longitudinal servo track pattern located on an elongated medium having other areas on which information are recorded and reproduced, said servo track pattern comprising a plurality of digital mark patterns recorded thereon which provide control signals to a control system that controls the position and velocity of the elongated medium relative to a magnetic reproducing head which reads information from the elongated medium, each of said digital mark patterns comprising:a leading identifier field of digital bits; a trailing identifier field of digital bits; and a field of digital synchronizing data located between said leading and trailing identifier fields, wherein the flux transition directions and locations of said bits in a first direction are predefined and wherein the locations of successive flux transitions in said trailing identifier field in a second direction are identical to the locations of successive flux transitions in said leading identifier field in said first direction, the direction of each successive flux transition of said trailing identifier field in said second direction being opposite the direction of each successive flux transition in said leading identifier field in said first direction.
 11. A digitally recorded longitudinal servo track pattern for an elongated magnetic recording medium of the type which has separate recordable and reproducible areas, said servo track pattern adapted to provide signals for a servo system which controls the position and velocity of the medium relative to a magnetic reproducing head adapted to read the digitally recorded longitudinal servo track pattern during movement of the medium in either of one of two directions, said servo track pattern comprising:a leading identifier field of digital bits; a trailing identifier field of digital bits; and a field of digital synchronizing data located between said leading and trailing identifier fields, wherein, during reproduction, said leading identifier field of digital bits is electrically equivalent, while the medium is moving in a first direction, to said trailing identifier field of digital bits, while the medium is moving in a second direction opposite to said first direction, and wherein the flux transition directions and locations of said bits in said first direction are predefined, and the locations of successive flux transitions in said trailing identifier field in said second direction are identical to the locations of successive flux transitions in said leading identifier field in said first direction, the direction of each successive flux transition of said trailing identifier field in said second direction being opposite the direction of each successive flux transition in said leading identifier field in said first direction. 